We characterize the conditions under which completing a Delaunay tessellation produces a connguration that is a nondegenerate Delaunay triangulation of an arbitrarily small perturbation of the original sites. One consequence of this result is a simple postpro-cessing step for resolving degeneracies in Delaunay triangulations that does not require symbolic perturbation of the data. We also give ...

The authors present a higher-order Godunov method for the solution of the twoand three-dimensional equations of ideal magnetohydrodynamics (MHD). This work is based both on a suitable operator-split approximation to the full multidimensional equations, and on a one-dimensional Riemann solver. TIlls Riemann solver is sufficiently robust to handle the nonstrictly hyperbolic nature of the MHD equa...

I review recent constraints on and claimed detections of a time-varying fine-structure constant α. Our results are consistent with no variation in α from the epoch of recombination to the present day, and restrict any such variation to be less than about 4%. The forthcoming MAP and Planck experiments will be able to break most of the currently existing degeneracies between α and other cosmologi...